Inverters: Grid-Tie
Grid-tie, or utility inter-tie, inverters convert DC power from
PV modules into AC power to feed into the utility grid.
There are two major types of grid-tie inverters: string
inverters and low voltage inverters.
String inverters are
wired together in series to achieve a higher voltage.
These inverters are designed to run at voltages up to 600
VDC. String wiring is faster to install, more
efficient and allows the use of smaller gauge wire. DC
voltage this high can be very dangerous and life
threatening, so string inverters should be installed and
serviced by qualified electricians.
A grid-tie PV system
uses the utility company, in effect, as its storage battery.
When the sun is shining, your electricity comes from the PV
array, via the inverter. If the PV array is generating
more power than you are using, the excess is sold to the
power utility company through your electric meter, by making
the meter run backwards. When you need more power than
the PV array can supply, the utility makes up the
difference. This type of system makes the most sense
in most cases where you have utility power, because there
are no batteries to maintain or replace.
Unfortunately, if the utility power goes down, this type of
inverter will go off too, regardless of whether or not the
sun is shining.
